Wonderfully, Brendan Farren of Big Green Art has a video showing how to make one of my favourite shapes (1) of Brigit's cross, the three-armed version once found frequently in byres. Now, I haven't tried his instructions. I'd love to hear how you do.
"How To Weave A Three Legged Brigid's Cross" by Brendan (Video)
Brendan teaches willow weaving from basics to some pretty awesome stuff. Have a look at his website and at the very least, if you are interested, download his free booklet, The Willow Handbook.
(1) See this post for a feast of Brigit's crosses from E. Estyn Evans.